Colorectal cancer is the second leading cause of cancer mortality in the United States. Most colorectal cancers arise in adenomatous polyps, and people who have had this type of polyp remain at increased risk of developing recurrent pre-cancerous polyps and cancer. Regular surveillance colonoscopy with removal of all detected polyps has been shown to decrease the incidence of colorectal cancer. Therefore, recent national guidelines recommend that individuals with a history of adenomatous polyps undergo repeat colonoscopy every 3 to 5 years. Compliance with these guidelines, however, may be less than optimal. This study will implement and evaluate a randomized intervention to improve surveillance for colorectal polyps at Brigham and Women's Hospital (BWH), a major academic medical center in Boston. The study has the following three specific aims: 1) To determine whether rates of surveillance colonoscopy can be substantially increased among patients with prior adenomatous polyps by linking computerized data from colonoscopy and pathology reports to identify patients with prior polyps who are due for repeat colonoscopy, and providing reminders to primary care physicians caring for these patients; 2) To assess whether patient demographic characteristics or site of primary care are associated with differences in baseline rates of surveillance colonoscopy among patients with prior polyps; and 3) To evaluate whether the impact of the study intervention varies by patient demographic characteristics or site of primary care, including hospital-based primary care practices, community-based primary care practices, community health centers, or an integrated multi-specialty group practice. This study will provide a model for evaluating how data from electronic medical records can be used to improve screening of patients with prior colorectal polyps who are at increased risk of developing recurrent polyps or cancer.